Clinical research and patient care would benefit greatly if a simple, safe method was available to measure continuous aortic flow and the aortic velocity profile in man. With such an instrument, aortic impedance could be determined continuously. The research proposed in this application is directed at developing and validating a second-generation doppler probe to measure continuous aortic flow and the aortic velocity profile in man. The probe whih is 2 mm in diameter would be sewn to the aortic adventitia at the time of open-heart surgery and removed by gentle traction two to five days following surgery. Aortic velocity would be measured simultaneously at 16 equidistant points across the aortic wall. This will allow us to compute aortic flow (mean aortic velocity x diameter) and to visualize the aortic velocity profile throughout the cardiac cycle. Preliminary studies indicate that the method is safe and that valid measurements will be obtainable. To further establish the validity of the second-generation doppler instrument, several animal studies will be done. Data obtained from the probe over a wide range of conditions will be compared with accepted methods (aortic flow -- electromagnetic flow meter; aortic diameter --sonomicrometer; aortic velocity profile -- hot film anomometer). After the safety and validity of the method has been assured, many exciting clinical studies will be undertaken.